Fuel Tank Float Arm Assembly

ABSTRACT

The invention concerns a float arm assembly for use in a vehicle fuel tank and a method of operating the float arm assembly to determine a level of fuel in the tank. First and second resistor cards are electrically connected in series and each includes a pivoting float arm with a float attached to an end. The first and second resistor cards, with separate floats allow the fuel level to be more accurately determined, especially in fuel tanks with complex contours and indentations in the tank wall that create dead bands in a single float type of arrangement.

BACKGROUND OF INVENTION

The present invention relates to a float arm assembly used for measuringthe liquid level in a fuel tank, and in particular to a float armassembly in a vehicle fuel tank.

A typical float arm assembly used in a vehicle fuel tank includes afixed support to which a ceramic resistor card is mounted. A float ispivotally mounted to the resistor card by a float arm. As the fuel levelin the tank goes up and down, the buoyancy of the float causes it tomove up and down with the level of fuel, thus changing the angle of thefloat arm relative to the resistor card. This change in angle causes achange in output from the resistor card, which is typically received andprocessed by a powertrain control module and displayed on the fuelgauge.

In modern automotive vehicles, the desire to maximize the capacity of afuel tank may require the fuel tank to have a greatly contoured shape.This may even include significant indentations in the fuel tank wall inorder to avoid adjacent vehicle structure and components. The contouredshape—in combination with the indentations—may limit the amount ofpivoting of the float and float arm that can occur without creatinginterference problems between the float arm assembly and the fuel tankwall. Consequently, the float and float arm may not be able to pivot allthe way up to a full liquid level and/or all the way down to an emptyliquid level. Such limitations in the travel of the float arm and float,then, create a dead band, which is the unreadable but useful fuel in thefuel tank. This dead band is undesirable because it limits the accuracyof the fuel gauge reading, which may reduce customer satisfaction withthe vehicle and possibly even increase warranty costs.

Attempts to minimize the dead band have included fuel tanks with twoseparate float arm assemblies, each mounted and operating separately.While this may reduce dead band concerns, it adds an additional senderopening for communicating the additional fuel level signal to thepowertrain control module. This multiple float arm assembly, then,requires the powertrain control module to receive and process a second,separate fuel level signal, adds additional cost for fabricating andassembling an entire separate float arm assembly and cover for thesecond sender opening, and increases the potential for permeation out ofthe tank.

SUMMARY OF INVENTION

An embodiment of the present invention contemplates a float arm assemblyfor a vehicle fuel tank. The float arm assembly comprises a first floatsupport mountable in the fuel tank, a second float support mountable inthe fuel tank, a first resistor card mounted to the first float support,a second resistor card mounted to the second float support, spaced fromthe first resistor card and electrically connected in series with thefirst resistor card, a first float arm pivotally connected to the firstresistor card and extending therefrom, a second float arm pivotallyconnected to the second resistor card and extending therefrom, a firstfloat fixed to the first float arm, and a second float fixed to thesecond float arm.

An embodiment of the present invention contemplates a float arm assemblyfor a vehicle fuel tank comprising: at least one float support mountablein the fuel tank; a first resistor card mounted to the at least onefloat support; a second resistor card mounted to the at least one floatsupport, spaced from the first resistor card and electrically connectedin series with the first resistor card; a first float arm pivotallyconnected to the first resistor card and extending therefrom; a secondfloat arm pivotally connected to the second resistor card and extendingtherefrom; a first float fixed to the first float arm; and a secondfloat fixed to the second float arm.

An embodiment of the present invention contemplates a method ofdetecting a level of a fuel in a vehicle fuel tank having a float armassembly, the method comprising the steps of: connecting a firstresistor card in electrical series connection with a second resistorcard that is spaced from the first resistor card; allowing a firstfloat, having a density less than the fuel, to pivot on a first floatarm relative to the first resistor card due to the buoyancy of the firstfloat in the fuel; allowing a second float, having a density less thanthe fuel, to pivot on a second float arm relative to the second resistorcard due to the buoyancy of the second float in the fuel; andcommunicating a signal indicative of a position of the first float armrelative to the first resistor card and a position of the second floatarm relative to the second resistor card to a powertrain control module.

An advantage of an embodiment of the present invention is that the deadband is greatly reduced or even eliminated, even with tanks havingcomplex contours and intrusive indentations. Thus, a more accurate fuelgauge reading over the entire fill level of the tank is provided.

An advantage of an embodiment of the present invention is that only onefuel level signal needs to be communicated from the tank to thepowertrain control module, even though two float arms and floats areemployed. Moreover, with resistor cards connected in series, thiscommunicated signal can be the same as with a tank having a single floatarm and float.

An additional advantage of an embodiment of the present invention isthat the more accurate fuel level reading is obtained without the needto add an additional float arm assembly, fuel sender hole and cover tothe fuel tank. Thus, increase potential for permeation is avoided, andadditional parts and assembly time are minimized.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a somewhat schematic, partial section view of a portion of afuel tank assembly, with floats shown in a full fuel tank position, inaccordance with the present invention.

FIG. 2 is a view similar to FIG. 1, but with the floats shown in anempty fuel tank position.

DETAILED DESCRIPTION

FIGS. 1-2 illustrate a fuel tank assembly, indicated generally at 20,for a vehicle (not shown). The fuel tank assembly 20 includes a tank 22(i.e., the tank wall and covers for openings in the tank walls), whichhas a complex shape needed to maximize the fuel capacity while fittingaround/between various vehicle components. For example, the tank 22includes a seat belt anchor indentation 24, which is needed for the tank22 to avoid interfering with a seat belt anchor (not shown). Also, forexample, the tank 22 has a rear suspension indentation 26 that allowsthe tank 22 to avoid interfering with the vehicle rear suspension (notshown). The tank 22 has an overall shape with a shorter horizontallyextending portion 28 and a taller vertically extending portion 30.Again, the shape is dictated to a great extent by the need to fit aroundvehicle structure and components (not shown). The examples justdiscussed are some of many examples of overall shapes and indentationsthat may be needed in order to allow for maximum capacity of a fuel tankwhile avoiding vehicle structure and components.

The fuel tank assembly 20 includes a float arm assembly 32 mountedtherein, having a main support 34 that extends generally vertically andis connected to a cover 36, which is mounted on and sealed to the top ofthe tank 22 (over a sender opening). The float arm assembly 32 alsoincludes a first float support 38, extending from the main support 34,and a second float support 40, which may extend from the main support 34or the first float support 38. While the first float support 38 andsecond float support 40 may be separate components, they also may be anintegral part with two separate resistor cards mounted spaced apart ifthe shape of the tank 22 for the particular vehicle allows for such aconfiguration. Preferably, the first float support 38 and the secondfloat support 40 are mounted on the same main support 34 so they move upand down by the same amounts as the floor of the tank 22 flexes due topressure fluctuations in the fuel tank 22. This mounting configuration,then, minimizes inaccuracies that can be introduced in fuel levelreadings.

The first float support 38 includes a first ceramic resistor card 42mounted to its end opposite the main support 34. A first float arm 44extends from and pivots relative to the first ceramic resistor card 42.A first float 46 extends from a free end of the first float arm 44. Thesecond float support 40 includes a second ceramic resistor card 48mounted to its end opposite the main support 34. A second float arm 50extends from and pivots relative to the second ceramic resistor card 48.A second float 52 extends from a free end of the second float arm 50.

The float supports 38, 40 and resistor cards 42, 48 remain fixed intheir positions in the tank 22 as the vehicle is operated. The floats46, 52 have a density less than the fuel in the tank 22 and so theirbuoyancy will cause them to float up and down with the changing fuellevel in the tank 22. As the floats 46, 52 float up and down with thechanging fuel level in the tank 22, they will cause the float arms 44,52 to pivot relative to their respective ceramic resistor cards 42, 48.The pivoting causes the resistance output of the particular resistorcard 42, 48 to vary, based on the angle of its float arm 44, 50.

The second float support 40 extends outward and upward farther from themain support 34 than the first float support 38. The length and angle ofextension of the second float support 40 locates the second ceramicresistor card 48 such that it will allow the second float 52 to freelypivot from at or near the highest level the fuel reaches for a full tank(indicated by dashed line 60 in FIG. 1) to a level where the tank 22 isonly partially filled with fuel. In the particular example of thisembodiment, the second float 52 is allowed to pivot down to a level thatis below that of the seat belt anchor indentation 24. Consequently,neither the seat belt anchor indentation 24 nor the rear suspensionindentation 26 restrict or inhibit the desired range of motion for thesecond float 52.

The length and angle of extension of the first float support 38 locatesthe first ceramic resistor 42 such that it will allow the first float 46to freely pivot from near the seat belt anchor indentation 24 to a levelwhere the tank 22 is almost completely empty of fuel (indicated bydashed line 62 in FIG. 2). Neither the seat belt anchor indentation 24nor the rear suspension indentation 26 restrict or inhibit the desiredrange of motion for the first float 46.

Ideally, the overlap between the lowest level to which the second float52 extends and the highest level to which the first float 46 extends iszero. Thus, as the fuel tank 22 empties, the second float 52 would stopas the first float 46 begins to drop. But due to manufacturingtolerances, there may be a small designed-in overlap zone, which ispreferably minimized based on manufacturing capability for theparticular fuel tank assembly 20.

The first and second ceramic resistor cards 42, 48 are preferably wiredin series (indicated schematically by dashed line 56), and incommunication with a powertrain control module 54. Thus, the powertraincontrol module 54 can receive a single signal from this fuel tankassembly 20 relating to the level of fuel in the tank 22. Also,preferably (but not required), the two resistor cards 42, 48 have atotal resistance equal to the resistance of a tank having a singlefloat. In this way, the powertrain control module 54 can be used for aone float or a two float configuration. With the resistor cards 42, 48wired in series, the overlap zone will provide a slight non-linearity inthe signal from the resistor cards 42, 48 when the fuel level is in theoverlap zone. But with the approximate amount of overlap known, thenon-linearity of the signal in this zone is accounted for in thecalibration of the powertrain control module 54.

FIG. 1 illustrates the positions of the floats 46, 52 when the level offuel 60 in the fuel tank 22 is at its highest. Both floats 46, 52 are attheir highest levels, so, with the resistor cards 42, 48 connected inseries, the total resistance is the sum of that from the two cards 42,48—this resistance indicating a full tank 22. FIG. 2 illustrates thepositions of the floats 46, 52 when the level of fuel 62 in the fueltank 22 is at its lowest. Both floats 46, 52 are at their lowest levels.Again, the total resistance is the sum of that from the two cards 42,48—this resistance indicating an empty tank. Between full and partiallyempty, the second float 52 will drop with the fuel level, while thefirst float 46 remains stationary, so the change in resistance of thesecond resistor card 48 will indicate a drop in fuel level.

Since the second float 52 extends essentially up to the full level 60and the first float 46 extends essentially down to the empty level 62,the amount of fuel in the tank 22 over the full range can be accuratelydetermined. This is true even though the contours and indentations inthe particular tank would otherwise prevent an accurate measurement froma float arm assembly with only a single float. Moreover, two separatefloat arm assemblies, with the extra hardware and multiple signals sentto the powertrain control module, are not required to obtain an accuratefuel level reading.

While only two resistor cards connected in series (with respective floatarms and floats) are shown in this embodiment, the float arm assemblycan have three or more cards connected in series (and correspondingfloat arms and floats) if needed to obtain accurate fuel level readingsfor particularly complicated shapes of fuel tanks. Also, for vehicleshaving saddle tanks, each of the saddle tanks can have multiple resistorcards if so desired, with the resistor cards in each respective tankconnected in series.

While certain embodiments of the present invention have been describedin detail, those familiar with the art to which this invention relateswill recognize various alternative designs and embodiments forpracticing the invention as defined by the following claims.

1. A float arm assembly for a vehicle fuel tank comprising: a firstfloat support mountable in the fuel tank; a second float supportmountable in the fuel tank; a first resistor card mounted to the firstfloat support; a second resistor card mounted to the second floatsupport, spaced from the first resistor card and electrically connectedin series with the first resistor card; a first float arm pivotallyconnected to the first resistor card and extending therefrom; a secondfloat arm pivotally connected to the second resistor card and extendingtherefrom; a first float fixed to the first float arm; and a secondfloat fixed to the second float arm.
 2. The assembly of claim 1including a main support supporting the first float support and thesecond float support in the fuel tank.
 3. The assembly of claim 1including a main support supporting the first float support, and thefirst float support supporting the second float support.
 4. The assemblyof claim 1 wherein the second float arm is pivotable relative to thesecond resistor card to an extent that allows the second float to extendupward adjacent to a full fuel level and downward partially toward anempty fuel level.
 5. The assembly of claim 4 wherein the first float armis pivotable relative to the first resistor card to an extent thatallows the first float to extend downward adjacent to the empty fuellevel and upward partially toward the full fuel level.
 6. The assemblyof claim 5 wherein the downward pivot of the second float arm allows thesecond float to be at the same level as the first float when the firstfloat arm is pivoted upward.
 7. The assembly of claim 1 including apowertrain control module wherein one of the first resistor card and thesecond resistor card is in communication with the powertrain controlmodule with a signal indicative of a sum of resistances of the firstresistor card and the second resistor card.
 8. A float arm assembly fora vehicle fuel tank comprising: at least one float support mountable inthe fuel tank; a first resistor card mounted to the at least one floatsupport; a second resistor card mounted to the at least one floatsupport, spaced from the first resistor card and electrically connectedin series with the first resistor card; a first float arm pivotallyconnected to the first resistor card and extending therefrom; a secondfloat arm pivotally connected to the second resistor card and extendingtherefrom; a first float fixed to the first float arm; and a secondfloat fixed to the second float arm.
 9. The assembly of claim 8including a main support supporting the at least one float support inthe fuel tank.
 10. The assembly of claim 8 wherein the second float armis pivotable relative to the second resistor card to an extent thatallows the second float to extend upward adjacent to a full fuel leveland downward partially toward an empty fuel level.
 11. The assembly ofclaim 10 wherein the first float arm is pivotable relative to the firstresistor card to an extent that allows the first float to extenddownward adjacent to the empty fuel level and upward partially towardthe full fuel level.
 12. The assembly of claim 8 wherein the first floatarm is pivotable relative to the first resistor card to an extent thatallows the first float to extend downward adjacent to the empty fuellevel and upward partially toward the full fuel level.
 13. The assemblyof claim 8 including a powertrain control module wherein one of thefirst resistor card and the second resistor card is in communicationwith the powertrain control module with a signal indicative of a sum ofresistances of the first resistor card and the second resistor card. 14.A method of detecting a level of a fuel in a vehicle fuel tank having afloat arm assembly, the method comprising the steps of: (a) connecting afirst resistor card in electrical series connection with a secondresistor card that is spaced from the first resistor card; (b) allowinga first float, having a density less than the fuel, to pivot on a firstfloat arm relative to the first resistor card due to the buoyancy of thefirst float in the fuel; (c) allowing a second float, having a densityless than the fuel, to pivot on a second float arm relative to thesecond resistor card due to the buoyancy of the second float in thefuel; and (d) communicating a signal indicative of a position of thefirst float arm relative to the first resistor card and a position ofthe second float arm relative to the second resistor card to apowertrain control module.
 15. The method of claim 14 wherein step (d)is further defined by the signal being a sum of resistances of the firstresistor card and the second resistor card.
 16. The method of claim 15wherein step (b) is further defined by the first float arm beingpivotable relative to the first resistor card to an extent that allowsthe first float to extend downward adjacent to an empty fuel level andupward partially toward a full fuel level.
 17. The method of claim 16wherein step (c) is further defined by the second float arm beingpivotable relative to the second resistor card to an extent that allowsthe second float to extend upward adjacent to the full fuel level anddownward partially toward the empty fuel level.
 18. The method of claim14 wherein step (b) is further defined by the first float arm beingpivotable relative to the first resistor card to an extent that allowsthe first float to extend downward adjacent to an empty fuel level andupward partially toward a full fuel level.
 19. The method of claim 18wherein step (c) is further defined by the second float arm beingpivotable relative to the second resistor card to an extent that allowsthe second float to extend upward adjacent to the full fuel level anddownward partially toward the empty fuel level.
 20. The method of claim19 wherein steps (b) and (c) are further defined by the downward pivotof the second float arm allowing the second float to be at the samelevel as the first float when the first float arm is pivoted upward.